Electric discharge device and operating circuits therefor



A ril 25, 1933. J. D. FORNEY 1,905,841

ELECTRIC DISCHARGE DEVICE AND OPERATING CIRCUITS THEREFOR Filed March 4, 1930 Patented Apr. 25, 1933 UNITED STATES.

PATENT OFFICE JOHN D. FORNEY, OF CHATEAM, NEW JERSEY, ASSIGNOR TO GENERAL ELEO'IRIC VAPOR LAMP COMPANY, OF HOIBOKEN, NEWJERSEY, A CORPORATION OF NEW JERSEY ELECTRIC DISCHARGE DEVICE AND OPERATING CIRCUITS T HEREFOR Application filed March 4,

The present invention relates to electric gaseous discharge devices, and particularly to electrical circuits for the starting and operation of discharge devices having filamentary cathode heaters in series with the discharge.

A particular object of the present invention is to provide an improved method of and means for starting and operating such devices. A further object of the invention is to provide means for rapidly heating the cathode during the starting period. Another object of the invention is to improve the stability of the discharge in such devices. Other objects and advantages of the invention will appear from the following'detailed specification, or from an inspection of the accompanying drawing.

It has been heretofore proposed to operate the filamentary cathode heaters of electric gaseous discharge devices by connecting them in series with the cathode whereby they would be heated by the discharge current. In starting such a device the filamentary heater is most conveniently energized by completing the circuit from the cathode-to an anode lead through a suitable resistance, but in order to avoid overheating of the filamentary heater and also toavoid rendering the ischa-rge unstable it is essential that this circuit should be broken as soon as the discharge is initiated, hence a series electromagnetic interrupter is usually provided. The inductive arc ballast, which has commonly been used as the magnet for this interrupter. has heretofore been invariably placed in the cathode lead withithe'result that the interrupter is immediately actuated by the. current passing through the filamen "tary heater, resulting in a. voltage surge on the cathode which initiates a discharge in the device before the cathode is properly heated.

Under such circumstances the discharge.

tends to concentrate at a hot spot on the cathode, frequently with destructive effect thereon. I have discovered that this difficulty may be avoided without the use of additional apparatus by placing the inductance ata pointin the circuit where it is. not traversed by this heating current; for r 1930. Serial No. 433,055.

example, in the anode lead, where direct current is employed. Where desired, auxiliary means is provided to momentarily energize this inductance, after a suitable time inter-- and because it is desirable to heat the stabilizing resistance, which usually has a lar positive thermal resistance characteristic, in order to bring it to normal operating temperaturebefore initiation of the discharge. In this case means are employed to open the filament circuit before an attempt is made to initiate the discharge in order that open circuit potential mayexist between the anode and cathode at the time of initiation of the discharge. I have also discovered that the period of delay required before a discharge is initiated in such a device may be appreciably shortened by means of additional heater capacity which is used only during startmg.-

While the ballast resistance used in series wit-h the discharge ordinarily has a high temperature coeflicient, and hence tends to stabilize the discharge despite fluctuations in the applied potential, it has been found that the Va ,iations in the heating of the cathode which iresult from even slight variations in the discharge current react to cause still greater variations in the discharge current, the effects thus being cumulative, so that such a device tends tobe relatively unstable in operation. I have discovered that this can be overcome by connecting asuitable resistor having a negative thermal resistance characteristic in parallel with the filamentary heater whereby thecurrent through said heater. is maintained substantially v.rx nstant. de-

spite variations in the discharge current.

preferably provide means for disconnecting said resistor during starting'in order ,to

hasten the heating thereof.

For the purpose of illustrating my inve'n v(It) arrangement of tion I have shown schematic diagrams of a number of embodiments thereof in, the accompanying drawing, in which Fig. 1 is a schematic diagram showing a circuit for energizing the filamentary heater of a gaseous discharge device on direct current,

Fig. 2 is a diagram of a modification of the circuit of Fig. 1 showing a more efiicient arrangement of the filamentary heater,

Fig. 3 is a schematic diagram of a circuit similar to that of Fig. 1, but having automatic discharge initiating means incorporated therein,

Fig. 4 is a diagram of a modification of the circuit of Fig. 3 showing the use of a resistor in parallel with the filamentary heater, with means for automatically disconnecting said resistor during starting,

Fig. 5 is a diagram of another modification of the circuit of Fig. 3, wherein. the heating Fig. 2 is incorporated,an

Fig. 6 is a schematic diagram showing a further modification of the circuit of Fig. 5.

In the drawing, with particular reference to Fig. 1, an electric gaseous discharge device 1, which contains any suitable gas such as neon or vapor such as mercury, has sealed therein an anode 2 of iron, graphite, or other suitable material and a cathode 3 of nickel or the like which is coated with an efficient electron emitter such as an alkali or alkaline earth oxide, said cathode preferably being in the form of a hollow cylinder or cone with a closed end. A filamentary heater 4 is position within said cathode with one end of said heater connected thereto. Leads 5 and 6 connect with said cathode 3 and with the free end of said heater 4 respectively, said lead 6 being connected directly to the negative terminal of a direct current source of suitable potential. The positive terminal of said source is connected throu h a resistance 7 and inductance 8 to said anode 2. From a point between said resistance 7 and said inductance 8 a connection is made through a resistance 9 and a mercury switch 10 to said lead 5. Said switch 10, of any usual type, is normally in a closed circuit position, but has an operating armature 11 in magnetic relation to said inductance 8, whereby said switch 10 is opened when said inductance is energized by current flow therethroug In, Fig. 2 the connections are similar to those of Fig. 1, save that an additional filamentary heater 4 heater 4 is likewise mounted within the cathode 3 with one end thereof connected to said cathode, the other end of said heater 4 being connected t the lead 5' which is in turn connected to one terminal of the switch 10.;

' The circuit of Fig. 3 differs from that (if Fig.1 only in the addition of automatic discharge initiating means. For this purpose a connection is'made from the lead 6'through' a mercury switch 12, resistance 13 of a thercharge in'the which is similar to the maintenance. of a mal delay unit and resistance 14 to the anode relation to a bimetallic element 15 which is deforned by heat therefrom to short circuit said resistance after current flow therethrough-for a predetermined time which is made to equal the time required to bring the cathode 3 to electron emitting temperature. The mercury switch 12 is preferably of the type commonly referred to as ashifter,since this type of switch opens the circuit therethrough in an abrupt manner, producing a higher potential surge from the inductance 8 thanwould a slower opening switch, and thereby facilitating the initiation of a disdevice 1. Said switch 12 which is also normally in a closed circuit position, is mechanically connected with the switch 10 in such a manner that upon actuation of the armature 11 said switch 12 is opened an instant after the opening of the switch 10.

Fig. 4 shows a modification of the circuit of Fig. 3 wherein a three electrode mercury switch 10', constituting a single pole double throw switch, is substituted for the switch 10 of Fig. 3. The third electrode of said switch 10 is connected through a resistance 16 to the lead 6, whereby said resistance 16, which has a negative temperature characteristic, is connected in parallel with the filamentary heater 4 as soon as the inductance 8 is energized. The circuit of Fig. 5 is. similar to that of Fig. 2 with the automatic discharge initiating circuit described in connection with Fig. 3 combined therewith.

Fig. 6 shows a modification of the circuit of Fig. 5 in which a four electrode mercury switch 10" is substituted for the switch 10 of Fig. 5, said switch having one electrode at one end thereof, another in the middle, and two electrodes normally insulated from each other at the opposite end of said switch. Said switch is normally in the position shown with the lead 5 connected to resistance 9, but' when actuated by the armature 11 the mercury flows to the opposite end of said switch, disconnecting the lead 5' from the resistance 9, and then connecting said lead to the lead 6 and to one end of the negative resistance 16, the other end of said resistance 16 being connected to the cathode 3, whereby the filamentaryheatersiand 4- are operated in series during the starting period, and in parallel with each other and with the resistance 16 during discharge. The action of the switches 10" and the switch 12 are so correlated, of course, that the circuit through resistance 9 is interrupted before opening 0 the switch 12.

In the use and operation of the apparatus illustrated in Fig. 1, upon connection to a suitable direct current source a current substantially equal to the 'normal discharge'curture 11 is attracted by the inductance 8, thus tilting the switches 10" and 12. The following sequence of operations is thereby produced. First the filament heating circuit through resistance 9 is interrupted in the. switch'lO". An instant thereafter the discharge initiating circuit is interrupted in the switch or shifter 12, the resulting potential surge from the inductance 8 being suflicient to initiate a discharge in the device 1, the

flow of the discharge current through the inductance 8 thereafter maintaining said mductance energized whereby said armature 1L is held adjacent thereto. At about the same time that the shifter 12 operates the continued motion of the switch 10" causes a circuit to be closed therein whereby lead 5' is connected to lead 6, heaters 4 and 4' being thereby con nected in parallel, but in series relation to the cathode 3, whereby saidcathode is continu-. ously heated by the flow of the dischargecurrent through said heaters. At substantially the same time the mercury also contacts with the electrode of said switch 10" which is connected to resistance 16, completing a circuit from lead 6 through switch 10 and resistance 16 to the cathode 3, said resistance 16 being thereby connected in parallel with the filamentary heaters 4 and 4'. Since this resistance has a negative character istic it is very eifective in maintaining the cathode 3 at a substantially constant temperature, as has been described in connmtion with the circuit of Fig. 4, the stabilityof the discharge being thereby greatly im roved.

While I have illustrated and escribed my invention by reference to several embodiments thereof, it is to be understood that various changes, substitutions and omissions within the scope of the appended claims may be made therein without departing from the spirit of my invention. J

I claim:

1. In combination, an electric discharge device having a thermionic cathode and an anode, a discharge maintaining circuit'for said device comprising leads from a suitable source of direct current to a point on said cathode and to said anode, an inductance in the lead to said anode, means to pass a heating cu rent through said cathode before a discharge is initiated in said device co'mprising a connection from another point on said cathode to said anode lead at a point between said inductance and said source, means to open said connection, and means to initiate a discharge in said device.

2. In combination, an electric gaseous discharge device having a thermionic cathode and an anode, a discharge maintaining circuit for said device comprising leads from a suitable source of direct current to a point onsaid cathode and to said anode, an inductance in the lead to said anode, means to ass a heatingcurrent through said cathode fore charge in said device.

mionic cathode, said cathode having an appreciable electrical resistance, a discharge mamtammg circuit for said device COIIIPIlS- ing leads from a suitable source of directv current to said anode and to a point on said cathode, an inductance in the lead to saidv anode, means to pass a; heating current through said cathode comprising a connection from another point on said cathode to said anode lead at a point between said inductance and said source, means responsive to current flow in said inductance, to open said connection, and means to initiate a dis- 4. In comb'natlon, an electric discharge device having an anode and a thermionic cathode, a discharge maintaining circuit therefor comprising leads from a suitable sourceof current to a point on said cathode and-to said anode, means to pass a heating current through said cathode before a discharge is initiated insaid device comprising a connection from another point on said cathode to the lead to said anode, a series inductance in a portion of said discharge maintaining circuit which is not traversed by said heating current during the starting period, and

means-responsive to current flow through said inductance to open the connection from said cathode to said anode lead.

, 5.. In combination, an electric gaseous discharge device having an anode, a thermionic cathode and a filamentary heater for said. cathode, one end of said heater being connected to. said cathode, a discharge maintaining circuit therefor comprising leads from a suitable source of direct current to said anode and the free end of said heater, an inductance in the lead to said anode, means to complete an auxiliary circuit to energize. sa d heater before a discharge is initiated in said device comprising a connection from said cathode to said anode lead at a point between said lnductance and said source, means to open .sald connection, and means to initiate a discharge in said device.

6. In combination, an electric gaseous dis-' charge device having an anode, a thermionic cathode and a filamentary heater for said cathode, one end of said heater being connected to said cathode, a discharge maintaining circuit therefor comprising leadsfrom a suitable "source of direct currentto said anode and to the free end of said heater, an inductance in the lead to said anode, means to complete an auxiliarycircuit to energize rent flows from the positive terminal through the resistance 7, resistance 9, mercury switch 10, lead 5, cathode L3, filamentary heater 4 and lead 6 back tothe negative terminal, said current heating said cathode 3 and resistance 7. At the same time the normal operating potential is applied between the anode 2 and cathode 3, but this potential is insuflicient to initiate a discharge therebetween, hence after said cathode 3 has attained its operating temperature the discharge is initiated in any usual manner, as by creating a high fr uency discharge in proximity to the device 1. The discharge current then passes through the circuit formed by resistance 7, inductance 8, anode 2, the discharge, cathode 3, heater 4 and lead 6. Armature 11 is thereupon attracted by said inductance 8, openin the switch 10, the filamentary heater 4 %eing thereafter heated by the discharge current, since said heater is in series with the cathode 3. Due to the fact that the resistance 7 which has a large positive temperature characteristic, has been in circuit with the cathode during the starting period the temperature thereof approaches that normally attained during operation, with the result that said resistance is immediately fully effective in limiting the discharge current, thereby eliminating the current surge which ordinarily occurs when the discharge is started.

The operation of the apparatus illustrated in Fig. 2 is similar to that described above. In this apparatus, however, the filamentary heaters 4 and 4' are in series during the startmg period, doubling the rate of heating of the cathode 3 without increasing the wattage required during the starting period. After the initiation of a discharge inthe device 1 the operation of the apparatus is identical with that described for Fig. 1, since then only the heater 4, in series with the cathode 3, is in circuit.

Upon application of a suitable D. C. potential to the apparatus of Fig. 3 a current flows through the filamentary heater 4 as heretofore described in connection with the apparatus of Fig. 1. A very small current, insuflicient to actuate the armature 11, likewise flows through the circuit including resistance 7, inductance 8, resistance 14, resistance 13, switch 12 and lead 6. This current passlng through the resistance 13 slowly heats up the bimetallic element 15,

warping said element until, after a time interval which is suflicient for the cathode 3 to attain operating temperature, the resistance 13 is short circuited by said element. The increased current which thereupon flows through the inductance 8 being sufiicient to attract the armature 11, the circuit through the switch 10 is thereupon interrupted, the voltage drop in the resistance 7 being materially decreased as a result'thereof. An instant later the cirthe collapsing magnetic field about the inductanceS thereupon producing a voltage surge of suflicient potential to initiate a disch. rge in the device 1. The inductance 8 is thereafter continuously energized by the discharge current so that the armature 11 is attracted thereto, said switches 10 and 12 being thereby both maintained in an open circuit position, the operation. of the device thereafter being the same as has been previously described in connection with Fig. 1.

The operation of the apparatus of Fig.4 is similar to that described in connection with Fig. 3 save for one feature. When the switch 10 is tilted by actuation of the armature 11- the resistance 16 is connected in parallel with'the filamentary heater 4. This resistance, which has a negative temperature characteristic, maintains the current through the heater 4 substantially constant despite variations in the discharge current, since any increase in the discharge current tends to increasethe temperature of both resistance 16 and heater 4, the ohmic value of resistance 16 thereupon decreasing while that of heater 4 increases, so that a larger proportion of the obvious that with suitably chosen constants the current variation in the heater 4 will be very small, the discharge being rendered thereby more stable.

With respect to the apparatus of Fig. 5, the operation thereof is identical with that of Fig. 3, except for the fact that a double filamentary heater, the operation of which was described in connection with Fig. 2, is used. Further description of the operation of thls ap aratus is therefore deemed unnecessary.

Epon the application of a suitable D. C. potential to the apparatus of Fig. 6 a current flows from the positive terminal through resistance 7, resistance 9, mercury switch 1 lead 5', heater 4', heater 4 and lead 6 to the negative terminal. This current is preferably substantially 50% of the normal d1scharge current, somewhat more than normal wattage due to the fact that the shunt resistance 16 is disconnected, being thereby supplied to said heaters 4 and 4' to heat the cathode 3, but may be somewhat greater where it is desired to decrease the time required to heat said cathode. A current likea by the action of the bimetallic element 15 in cult through the switch or shifter 12 is opened,

short circuiting the res stance 13 the armasaid device comprising a connection from said cathode to said anode lead at a point between said inductance and said source, means responsive to current flow through said induc-- fore a discharge is initiated in said device comprising a connection from another point on said cathode to said anode lead at a point between said inductance and said source, means responsive tocurrent flow through said inductance to open said last mentioned connection and means to initiate a discharge in said device after said cathode has reached operating temperature.

8. In combination, an electric gaseous discharge device having an anode and athermionic cathode, a discharge maintaining circuit therefor comprising leads from a suitable source of direct current to said anode and to another point on said cathode, an inductance in the-lead to said anode, means to complete an auxiliary circuit to heat said cathode before a discharge is initiated in said device comprising a connection from another point on said -cathode to said anode lead at a point between said inductance and said source, a resistance-in common with said last mentioned circuit and with said discharge maintaining circuit and means to open said cathode heating auxiliary. circuit after said cathode has reached operating temperature.

9. In combination, an electric gaseous discharge device having an anode, a cathode adapted to emit electrons when heated, a discharge maintaining circuit therefor comprising leads from a suitable source of direct current to said anode and to another point on said cathode, an inductance inthe lead-to said anode, meansxto complete an auxiliary circuit to heat said cathode before a discharge is initiated in said device comprising a connection from another point on said cathode to said anode lead at a point between said inductance and said source, a resistance in'common with said last mentioned circuit and with said discharge maintaining circuit, means'toopen said cathode heating auxiliary circuit after said cathode has reached operating temperature and means operative thereafter to initiate a discharge in said device.

' 10. In combination, an electric .gaseous discharge device having an anode, a cathode adapted to emit electrons when heated and two heaters for said cathode, one end of each of said heaters being connected to said cathode, a discharge maintaining circuit there for comprising leads'from a suitable source of direct current tosaid anode and to the free end of one of said heaters, an inductance in the lead to said'anode, means to complete an auxiliary circuit to energize said heaters comprising a connection from the free end of the second heater to said anode lead at a point between said inductance and said source, and means to open said connection.

11. In combination, an electric. gaseous discharge device having an anode, a cathode adapted to emit electrons when heated and two heaters for said cathode, one end of each of said heaters being connected to said cathode, a discharge maintaining circuit therefor comprising leads from a suitable source of direct current to said anode and to the free end of one of said heaters, an inductance in the lead to said anode, means to complete an auxiliary circuit to energize said heaters comprising a connection from the free end of the second heater to said anode lead at a point between said inductance and said source, means to oped-said last mentioned connection, and means to connect the free ends of said heaters together. v a

12. In combination, an electric gaseous dis charge device having an anode, a cathode adapted to emit electrons when heated, andmeans to heat said cathode, said means being in series with the discharge path within said device, and means to shunt a variable proportion of the discharge current from said heatingmeans, whereby the current through said heating means .is maintained substantially constant.

13. In combination, 7 an electric gaseous discharge device having an anode, a cathode adapted to emit electrons when heated, means to heat said cathode, said means being in series with the discharge path within said device, and a. resistance having a negative thermal coefiicient of resistivity in parallel with said heating means.

14. In combination, an electric gaseous discharge device having an anode, a cathode adapted to emit electrons when heated, means means to heat said cathode, said. means being in series with the discharge path within said device, a resistance having'a negative ther- I mal coefiicient of resistivity in parallel with said means and means to open the circuit through said resistance.

15. In combination, an electric gaseous discharge device having an anode, a cathode adapted to emit electrons when heated, and a heater for said cathode, one end of said heater being connected to said cathode,,a discharge maintaining circuit therefor comprise ing leads froma suitable source of current 'to said anode and to the free end of said anode, a resistance having a negative thermal coefficient of resistivity, and'means responsiveto current flow through said inductance to connect said resistance in parallel with said heater.

16. In combination, an electric gaseous dischar e device having an anode, a cathode adapte to emit electrons when heated, and

two heaters for said cathode, one end of each of saidheaters being connected to said cathode, a discharge maintainin circuit therefor comprising leads from a suitable direct current source to said anode and to the free end of one of said heaters, an inductance in the lead to said anode, means to complete an auxiliary circuit to energize said heaters comprising a connection from the free end of the second of said heaters to said anode lead at a point'betwe'en said inductance and neeaaaa cathode, which comprises closing a circuit through said heating means, opening said circuit after a predetermined time, initiating a dischar e in said device, and diverting a portion 0 the discharge current from said heating means during operation of the device.

Signed at Hoboken, in the county of Hudson and State of New Jersey, this 3d day of March, A. D. 1930.

JOHN D. FORNEY.

said source, a resistance in common with said discharge maintaining circuit and with said auxiliary circuit, means to open said con-- nection after a predetermined time interval,

cathode to pass a heating current thercthrough, opening said circuit after a prede: termined time, and initiating a discharge in said device. i

18. The 'method of starting an electric gaseous discharge device having an anode, a cathode adapted to emit electrons when heated, and a ballast resistance in series with the discharge path, which comprises closing a circuit through said cathode and said resistance, opening said circuit after a predetermined time, and thereafter initiating a discharge in said device.

19. The method of operating an electric gaseous discharge device having an anode,

a cathode adapted to emit electrons when heated, and means in series with the discharge pathin said device to heat said cathode, which comprises diverting a variable portion of the discharge current from said heatin means -to maintain "the current throug said heating means' substantially constant despite variations in the discharge current." I h 20. The method of starting-and operating an'electric gaseous discharge device having an anode, a cathode adapted tolemit electrons when heated," and means in series with the discharge .path in said device to heat said 

